Each year, respiratory syncytial virus (RSV) infects 4-5 million children in the US, and is the leading cause of infant hospitalizations (˜150,000 hospitalizations). Globally, it accounts for 6.7% of deaths in infants less than 1 year old, second only to malaria. In addition, it poses a serious threat to other high-risk groups, including elderly and immuno-compromised subjects, where it results in approximately an additional 180,000 hospitalizations and 12,000 deaths in the US. There are no current frontline treatments for RSV, and the only currently approved prophylactic treatment for RSV is passive administration of the licensed monoclonal antibody Synagis (palivizumab), which recognizes the RSV fusion (F) protein, and reduces incidence of severe disease by only ˜50%. The high cost of prophylaxis with Synagis limits its use only to premature infants and infants less than 24 months old with congenital heart disease. For a review see Costello et al., “Targeting RSV with Vaccines and Small Molecule Drugs, Infectious Disorders,” Drug Targets, 2012, vol. 12, no. 2. The development of a more effective and, ideally, more cost-effective RSV vaccine would be of enormous value. Clinical evidence that RSV F protein-specific antibodies can protect against disease has prompted a concerted effort to identify additional and better monoclonal antibodies, and to develop a protective vaccine to address this significant unmet medical need.